The Constitution mandates that the President takes the oath of office on January 20th. Since that fell on a Sunday, the public inauguration takes place tomorrow, January 21, 2013.
Watch the Obama family together at the moment:
President Obama took the oath, administered by Chief Justice John Roberts, in the Blue Room of the White House, using a bible that belonged to First Lady Michelle Obama’s paternal grandparents.
Vice President Biden was sworn in by Justice Sonia Sotomayor in front of family and friends in a ceremony at the Naval Observatory. Vice President Biden took the oath using the Biden family bible.